Solar heat collector, solar heat collecting multilayer sheet, and solar heat heater

ABSTRACT

A solar heat collector includes a heat collecting board, a solar radiation absorbing layer provided at one surface in a thickness direction of the heat collecting board, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2013-152881 filed on Jul. 23, 2013, the contents of which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solar heat collector, a solar heat collecting multilayer sheet, and a solar heat heater, to be specific, to a solar heat collector, a solar heat collecting multilayer sheet, and a solar heat heater including the solar heat collector and the solar heat collecting multilayer sheet.

2. Description of Related Art

It has been conventionally known that a solar heat heater such as a solar water heater is provided with a heat collector; the heat collector is heated by absorbing sunlight; and water (a heat medium) at the inside of the heat collector is heated, so that hot water is obtained.

In the heat collector (a heat collecting structure), it is required that heat absorbed by the heat collector fails to escape to the outside, that is, the heat emitting properties are reduced.

For example, a heat collecting structure of a solar heat collecting device provided with a heat absorber and a filter that is disposed at spaced intervals to the upper side thereof and reflects an infrared ray has been proposed (ref: for example, Japanese Unexamined Patent Publication No. H06-201197). In the heat collecting structure in Japanese Unexamined Patent Publication No. H06-201197, the heat emitting properties of the heat collecting structure are reduced by a space layer (a gap) divided between the heat absorber and the filter and the filter.

Also, a heat collecting structure of a solar water heater provided with a heat collector and a special metal film for Low-E (low emissivity) that is disposed at spaced intervals to the upper side thereof has been proposed (ref: for example, Japanese Unexamined Patent Publication No. 2004-176966). In the heat collecting structure of Japanese Unexamined Patent Publication No. 2004-176966, the heat collector is made of a metal board and the upper surface of the metal board is covered with a material (a cover layer) that promotes absorption of sunlight. The special metal film is also disposed at spaced intervals to the upper side of the cover layer. In Japanese Unexamined Patent Publication No. 2004-176966, the heat emitting properties of the heat collecting structure are reduced by a space layer (a gap) divided between the cover layer and the special metal film and the special metal film.

SUMMARY OF THE INVENTION

The filter in Japanese Unexamined Patent Publication No. H06-201197 may absorb sunlight and in such a case, heat generated in the filter is required to be effectively used. In Japanese Unexamined Patent Publication No. H06-201197, however, there is a disadvantage that the heat generated in the filter is not capable of being efficiently thermally conducted from the filter to the heat absorber due to the space layer (the gap) between the filter and the heat absorber and thus, the heat collecting structure is not capable of satisfying the above-described requirement.

In Japanese Unexamined Patent Publication No. 2004-176966, the special metal film may absorb sunlight and in such a case, heat generated in the special metal film is required to be effectively used. In Japanese Unexamined Patent Publication No. 2004-176966, however, there is a disadvantage that the heat generated in the special metal film is not capable of being efficiently thermally conducted from the special metal film to the heat collector due to the space layer (the gap) between the special metal film and the heat collector and thus, the heat collecting structure is not capable of satisfying the above-described requirement.

It is an object of the present invention to provide a solar heat collector that is capable of effectively using heat generated in a low emissivity and low solar reflectance layer, a solar heat collecting multilayer sheet, and a solar heat heater.

A solar heat collector of the present invention includes a heat collecting board, a solar radiation absorbing layer provided at one surface in a thickness direction of the heat collecting board, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.

In the solar heat collector of the present invention, it is preferable that the low emissivity and low solar reflectance layer has an emissivity of 0.75 or less and has a solar reflectance of 50% or less.

In the solar heat collector of the present invention, it is preferable that the low emissivity and low solar reflectance layer is prepared from a conductive ceramic.

A solar heat heater of the present invention includes the above-described solar heat collector.

A solar heat collecting multilayer sheet of the present invention includes a substrate sheet, a solar radiation absorbing layer provided at one surface in a thickness direction of the substrate sheet, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.

In the solar heat collecting multilayer sheet of the present invention, it is preferable that the low emissivity and low solar reflectance layer has an emissivity of 0.75 or less and has a solar reflectance of 50% or less.

In the solar heat collecting multilayer sheet of the present invention, it is preferable that the low emissivity and low solar reflectance layer is prepared from a conductive ceramic.

A solar heat collector of the present invention includes the above-described solar heat collecting multilayer sheet and a heat collecting board provided at the other surface in a thickness direction of a substrate sheet in the solar heat collecting multilayer sheet.

A solar heat heater of the present invention includes the above-described solar heat collector.

A solar heat heater of the present invention is preferably used as a solar water heater.

According to the solar heat collector of the present invention, the solar radiation absorbing layer absorbs sunlight and heat is generated, and the heat is capable of being efficiently thermally conducted to the heat collecting board.

The low emissivity and low solar reflectance layer reduces the reflection of sunlight and the sunlight is capable of surely reaching the solar radiation absorbing layer.

When the low emissivity and low solar reflectance layer absorbs sunlight and heat is generated, the low emissivity and low solar reflectance layer is provided at one surface in the thickness direction of the solar radiation absorbing layer, so that the heat is capable of being efficiently thermally conducted to the heat collecting board via the solar radiation absorbing layer.

Thus, the solar heat collector of the present invention is capable of effectively using sunlight and effectively collecting heat.

According to the solar heat collector of the present invention in which the substrate sheet in the solar heat collecting multilayer sheet of the present invention is laminated at the heat collecting board, the solar radiation absorbing layer absorbs sunlight and heat is generated, and the heat is capable of being efficiently thermally conducted to the heat collecting board via the substrate sheet.

When the low emissivity and low solar reflectance layer absorbs sunlight and heat is generated, the low emissivity and low solar reflectance layer is provided at one surface in the thickness direction of the solar radiation absorbing layer, so that the heat is capable of being efficiently thermally conducted to the heat collecting board via the solar radiation absorbing layer and the substrate sheet.

Thus, the solar heat collector of the present invention is capable of effectively using sunlight and effectively collecting heat.

Furthermore, the solar heat heater of the present invention includes the above-described solar heat collector, so that the heat medium is capable of being efficiently heated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a solar heat collector that is one embodiment of the present invention.

FIG. 2 shows a plan view of a solar water heater including the solar heat collector in FIGS. 1 and 5.

FIG. 3 shows a sectional view along an A-A line of the solar water heater in FIG. 2.

FIG. 4 shows a sectional view along a B-B line of the solar water heater in FIG. 2.

FIG. 5 shows a sectional view of a solar heat collector and a solar heat collecting multilayer sheet that are the second embodiment of the present invention.

FIG. 6 shows a sectional view along an A-A line of the solar water heater in FIG. 2.

FIG. 7 shows a sectional view along a B-B line of the solar water heater in FIG. 2.

FIG. 8 shows a sectional view of a solar heat collector in Comparative Example 4.

FIGS. 9 A to D show a heat collecting box for measuring a surface temperature of a solar heat collector:

FIG. 9A illustrating a heat collecting box that measures a heat collector in Examples 1 to 6 and Comparative Examples 2 to 3,

FIG. 9B illustrating a heat collecting box that measures a heat collector in Example 7,

FIG. 9C illustrating a heat collecting box that measures a heat collector in Comparative Example 1, and

FIG. 9D illustrating a heat collecting box that measures a heat collector in Comparative Example 4.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

In FIG. 1, the upper side of the paper surface is referred to as the upper side (one side in a first direction, one side in a thickness direction); the lower side of the paper surface is referred to as the lower side (the other side in the first direction, the other side in the thickness direction); the left side of the paper surface is referred to as the left side (one side in a second direction perpendicular to the first direction); the right side of the paper surface is referred to as the right side (the other side in the second direction); the front side of the paper surface is referred to as the front side (one side in a third direction perpendicular to the first and second directions); and the back side of the paper surface is referred to as the rear side (the other side in the third direction). To be specific, directions are in conformity with direction arrows in FIG. 1. Directions in FIG. 2 and the subsequent figures are in conformity with the directions in FIG. 1. In FIG. 2, a protective layer 9 to be described later is omitted so as to clearly show the relative arrangement of a hot water portion 7 and a casing 8 to be described later. Furthermore, in FIG. 2, a hot water storage portion 20 to be described later is shown by hatching so as to clearly show its shape.

As shown in FIG. 1, a solar heat collector 1 that is one embodiment of the present invention is formed into a flat plate shape extending in a plane direction (a direction perpendicular to the thickness direction). The solar heat collector 1 includes a heat collecting board 2, a solar radiation absorbing layer 3 that is provided on the upper surface (one surface in the thickness direction) of the heat collecting board 2, and a low emissivity and low solar reflectance layer 4 that is provided on the upper surface (one surface in the thickness direction) of the solar radiation absorbing layer 3.

The heat collecting board 2 is provided in the lower portion (the other end portion in the thickness direction) in the solar heat collector 1. The heat collecting board 2 is configured to be capable of conducting heat conducted from the solar radiation absorbing layer 3 and the low emissivity and low solar reflectance layer 4 to be described next to water, when used in a solar water heater 6 (ref: FIG. 3) to be described later. The shape in plane view of the heat collecting board 2 is formed to be the same as that in plane view of the solar heat collector 1. An example of a heat collecting material that forms the heat collecting board 2 includes a metal material such as aluminum, copper, iron, chromium, or alloys thereof (to be specific, stainless steel or the like). Preferably, aluminum and stainless steel are used. The heat collecting board 2 has a thickness of, for example, 0.1 mm or more, or preferably 0.5 mm or more, and of, for example, 5 mm or less, or preferably 2 mm or less.

The solar radiation absorbing layer 3 is provided at a midway of the thickness direction in the solar heat collector 1 and is provided on the entire upper surface of the heat collecting board 2. The solar radiation absorbing layer 3 is configured to be capable of generating heat by efficiently absorbing sunlight and achieving heat insulating effect (having low emissivity). An example of a solar radiation absorbing material that forms the solar radiation absorbing layer 3 includes a selectively absorbing material described in Japanese Unexamined Patent Publication No. 2004-176966. To be specific, examples thereof include black chromium, black nickel, and gold-magnesium oxide cermet. An example of the solar radiation absorbing material also includes a coating film prepared from a black coating material such as SiZrO₄, Cr₂O₃, and an iron oxide-based inorganic pigment. The solar radiation absorbing layer 3 has a thickness of, for example, 2 to 10 μm, when the solar radiation absorbing layer 3 is prepared from a selectively absorbing material, and of, for example, 20 to 80 μm, when the solar radiation absorbing layer 3 is prepared from a coating film.

The low emissivity and low solar reflectance layer 4 is provided in the upper portion (one end portion in the thickness direction) in the solar heat collector 1 and is provided on the entire upper surface of the solar radiation absorbing layer 3. The low emissivity and low solar reflectance layer 4 is provided so as to be in contact with the upper surface of the solar radiation absorbing layer 3. The low emissivity and low solar reflectance layer 4 is configured to allow sunlight to reach the solar radiation absorbing layer 3, that is, not to block the sunlight applied from the upper side and to be capable of reflecting the heat generated in the solar radiation absorbing layer 3 toward the lower side. In other words, the low emissivity and low solar reflectance layer 4 is configured to reduce the emissivity of the solar heat collector 1 and to reduce the solar reflectance of the solar heat collector 1. A material that forms the low emissivity and low solar reflectance layer 4 is not particularly limited as long as it is a material that achieves the above-described function. An example thereof includes a conductive ceramic.

Examples of the conductive ceramic include ITO (Indium Tin Oxide, tin-doped indium oxide or indium tin oxide), ATO (Antimony Tin Oxide, tin-doped antimony oxide or antimony tin oxide), FTO (Fluorine Tin Oxide, fluorine-doped tin oxide), and IZO (Indium Zinc Oxide, zinc-doped indium oxide). In view of material cost, preferably, ITO is used.

The low emissivity and low solar reflectance layer 4 has an emissivity of, for example, 0.75 or less, preferably 0.60 or less, or more preferably 0.50 or less, and of, for example, 0.01 or more. When the emissivity of the low emissivity and low solar reflectance layer 4 is above the above-described upper limit, there may be a case where a function of reflecting the heat generated in the solar radiation absorbing layer 3 is poor such as in the case of an insulating ceramic (to be specific, SiO₂ or the like, ref: Comparative Example 2). The emissivity of the low emissivity and low solar reflectance layer 4 is described in the evaluation column of Examples later.

The low emissivity and low solar reflectance layer 4 has a solar reflectance of, for example, 50% or less, preferably 25% or less, or more preferably 10% or less, and of, for example, 0.11% or more. When the solar reflectance of the low emissivity and low solar reflectance layer 4 is above the above-described upper limit, there may be a case where sunlight is remarkably reflected and the sunlight is blocked to reach the solar radiation absorbing layer 3 such as in the case of a metal layer (to be specific, a silver alloy or the like, ref: Comparative Example 3). The solar reflectance of the low emissivity and low solar reflectance layer 4 is measured as a solar reflectance in a region of near infrared ray (780 to 2500 nm). The details are described in the evaluation column of Examples later.

The thickness of the low emissivity and low solar reflectance layer 4 is not particularly limited. In Patent Documents 1 and 2, the thickness of the low emissivity and low solar reflectance layer 4 is required to be formed as thin as possible so as to transmit much of sunlight therethrough. In this embodiment, however, the low emissivity and low solar reflectance layer 4 is not necessarily required to be formed thin, that is, is capable of being formed thick. Thus, a degree of freedom in selection of the material and the producing method of the low emissivity and low solar reflectance layer 4 is capable of being improved. To be specific, the low emissivity and low solar reflectance layer 4 has a thickness of, for example, 50 nm or more, or preferably 200 nm or more, and of, for example, 1000 nm or less, or preferably 600 nm or less. When the thickness of the low emissivity and low solar reflectance layer 4 is not more than the above-described upper limit, excessive reflection of sunlight in the low emissivity and low solar reflectance layer 4 is capable of being prevented. When the thickness of the low emissivity and low solar reflectance layer 4 is not less than the above-described lower limit, the reflectivity of heat (the heat reflectivity) generated in the solar radiation absorbing layer 3 is capable of being improved.

The solar heat collector 1 has a thickness of, for example, 0.1 mm or more, or preferably 0.5 mm or more, and of, for example, 5 mm or less, or preferably 2 mm or less.

Next, a method for producing the solar heat collector 1 is described with reference to FIG. 1.

In this method, first, the heat collecting board 2 is prepared.

Next, in this method, the solar radiation absorbing layer 3 is laminated on the upper surface of the heat collecting board 2. When the solar radiation absorbing layer 3 is prepared from a selectively absorbing material, the solar radiation absorbing layer 3 is formed on the upper surface of the heat collecting board 2 by, for example, an electrochemical treatment such as plating or anodic oxidation. On the other hand, when the solar radiation absorbing layer 3 is made of a coating film, for example, a black coating material is applied to the upper surface of the heat collecting board 2 to be thereafter, if necessary, dried, so that the solar radiation absorbing layer 3 is formed on the upper surface of the heat collecting board 2.

In this method, thereafter, the low emissivity and low solar reflectance layer 4 is directly formed on the upper surface of the solar radiation absorbing layer 3. Examples of a forming method of the low emissivity and low solar reflectance layer 4 include a sputtering method, a CVD method, a vacuum deposition method, an AD method, and an application method of a dispersion liquid of conductive nanoparticles (to be specific, particles in nano size prepared from a conductive ceramic). Preferably, a sputtering method is used.

Next, the solar water heater 6, as a solar heat heater, using the solar heat collector 1 is described with reference to FIGS. 2 to 4.

In FIGS. 2 and 3, the solar water heater 6 includes the casing 8, the hot water portion 7, and the protective layer 9 (ref: FIG. 3).

The casing 8 is, for example, configured to be capable of being disposed on a roof of a building. The casing 8 is formed into a generally rectangular shape in plane view, a thin flat shape in an up-down direction, and a bottomed box shape having an opening upwardly. In the upper portion of the casing 8, a first opening 16 is formed. Second openings 17 that correspond to a water supply port 14 and a water discharge port 15 to be described later are formed at the left-side wall and the right-side wall of the casing 8. The casing 8 has a double structure of an inner-side layer formed of, for example, a known heat insulating material such as a foamed material and an outer-side layer disposed at the outer side of the inner-side layer and formed of a metal material.

The hot water portion 7 is housed in the casing 8. The hot water portion 7 is disposed so that the projected surface thereof is overlapped with the first opening 16 of the casing 8, when projected in the up-down direction. The hot water portion 7 is made of an upper board 11 and a lower board 12 that extend in a direction perpendicular to the up-down direction (a plane direction). Each of the upper board 11 and the lower board 12 is formed into a shape integrally including flat plate portions 18 and curved portions 19 by forming a flat plate prepared from the above-described heat collecting material by pressing or the like.

In the upper board 11 and the lower board 12, a plurality of the flat plate portions 18 are formed at spaced intervals to each other in a front-rear direction and are formed into strip shapes extending in a right-left direction. In the upper board 11 and the lower board 12, the curved portions 19 are formed so as to connect the flat plate portions 18 that are adjacent thereto in the front-rear direction. That is, a plurality of the curved portions 19 are formed at spaced intervals to each other in the front-rear direction. In the upper board 11, the curved portions 19 are formed so as to protrude upwardly from the flat plate portions 18. To be specific, the curved portions 19 are, in side view, formed into generally semi-circular shapes expanding upwardly. The curved portion 19 of the lower board 12 is formed symmetrically in the up-down direction to the curved portion 19 of the upper board 11 with respect to the surface including the flat plate portion 18.

Each of the front end portions and the rear end portions of the upper board 11 and the lower board 12 is formed of the flat plate portion 18.

In the hot water portion 7, the upper board 11 and the lower board 12 are attached to each other so that the flat plate portions 18 of each of the upper board 11 and the lower board 12 are in contact with each other, so that the hot water storage portions 20 are divided by the curved portions 19 of the upper board 11 and the lower board 12. The hot water storage portions 20 are formed into generally cylindrical shapes extending in the right-left direction. The flat plate portions 18 of the upper board 11 and the lower board 12 are in contact with each other so that water in the hot water storage portions 20 fails to leak to the outside and in this way, each of the hot water storage portions 20 with its inside sealed is formed. A plurality of the hot water storage portions 20 are adjacently disposed in the front-rear direction corresponding to a plurality of the curved portions 19 that are adjacently disposed in the front-rear direction. The hot water storage portions 20 that are adjacent to each other are connected by connecting tubes 22. The connecting tubes 22 connect the left end portions of the hot water storage portions 20 that are adjacent to each other in the front-rear direction and also connect the right end portions of the hot water storage portions 20 that are adjacent to each other in the front-rear direction. Thus, in the hot water storage portions 20 and the connecting tubes 22, a path in a zigzag shape in plane view is formed.

The water supply port 14 and the water discharge port 15 are connected to the hot water portion 7. The water supply port 14 is configured to be capable of supplying water to the inside of the hot water storage portions 20. On the other hand, the water discharge port 15 is configured to be capable of discharging (supplying) hot water obtained in the hot water storage portions 20 to the outside. To be specific, the water discharge port 15 is connected to the hot water storage portion 20 at the right end portion of the rear end portion, while the water supply port 14 is connected to the hot water storage portion 20 at the left end portion of the front end portion.

As shown in FIGS. 3 and 4, the upper board 11 is made of the heat collecting board 2 of the solar heat collector 1. That is, the upper board 11 corresponds to the heat collecting board 2 of the solar heat collector 1 described in FIG. 1 and the solar radiation absorbing layer 3 and the low emissivity and low solar reflectance layer 4 are sequentially disposed on the heat collecting board 2. The lower board 12 is also made of the heat collecting board 2 of the solar heat collector 1.

Accordingly, the hot water portion 7 is formed from the same material as that of the heat collecting board 2 described above. The thickness of the upper board 11 and the lower board 12 is the same as that of the heat collecting board 2 described above.

The protective layer 9 is a layer that protects the solar heat collector 1 and transmits sunlight therethrough. The protective layer 9 is, for example, formed from a transparent material such as glass and is disposed in opposed relation at spaced intervals to the upper side of the solar heat collector 1. The protective layer 9 is put at the upper end surface of the casing 8 so as to cover the opening 16. The thickness of the protective layer 9 is appropriately set.

In order to fabricate the solar water heater 6, two flat plates that constitute the heat collecting board 2 of the solar heat collector 1 are prepared. Next, each of the two flat plates is formed into a shape having the curved portions 19 and the flat plate portions 18 by pressing or the like, so that the upper board 11 and the lower board 12 are fabricated. Thereafter, the upper board 11 and the lower board 12 are attached to each other so that the flat plate portions 18 of each of the upper board 11 and the lower board 12 are in contact with each other and the hot water storage portions 20 are formed. Simultaneously, the connecting tubes 22 are installed in the upper board 11 and the lower board 12. In this way, the hot water portion 7 is fabricated.

Thereafter, the water supply port 14 and the water discharge port 15 are inserted into the second opening 17 to be installed in the upper board 11 and the lower board 12, while the hot water portion 7 is put on the bottom wall of the casing 8 to be housed at the inside of the casing 8.

Thereafter, the protective layer 9 is laminated at the upper side of the casing 8.

In this way, the solar water heater 6 including the casing 8, the hot water portion 7, and the protective layer 9 is obtained.

In the solar water heater 6, water (water before being heated, to be specific, cold water) is supplied from the water supply port 14 to the hot water storage portions 20. When sunlight transmits through the protective layer 9 to be absorbed in the solar heat collector 1 of the upper board 11, heat is generated in the solar heat collector 1 and in this way, water in the hot water storage portions 20 is heated, so that hot water is obtained. The hot water is discharged to the outside via the water discharge port 15.

According to the solar heat collector 1, the solar radiation absorbing layer 3 absorbs sunlight and heat is generated, and the heat is capable of being efficiently thermally conducted to the heat collecting board 2.

The low emissivity and low solar reflectance layer 4 reduces the reflection of the sunlight and the sunlight is capable of surely reaching the solar radiation absorbing layer 3.

When the low emissivity and low solar reflectance layer 4 absorbs the sunlight and the heat is generated, the low emissivity and low solar reflectance layer 4 is formed on the upper surface of the solar radiation absorbing layer 3, so that the heat is capable of being efficiently thermally conducted to the heat collecting board 2 (the upper board 11) via the solar radiation absorbing layer 3.

Thus, the solar heat collector 1 is capable of effectively using the sunlight and effectively collecting the heat.

As a result, the solar water heater 6 includes the above-described solar heat collector 1, so that water is efficiently heated and hot water is capable of being efficiently obtained.

In the solar heat collector 1, when the low emissivity and low solar reflectance layer 4 has an emissivity of 0.75 or less and has a solar reflectance of 50% or less, a function of reflecting the heat generated in the solar radiation absorbing layer 3 is sufficiently ensured and the reflection of the sunlight is reduced, so that the sunlight is capable of surely reaching the solar radiation absorbing layer 3.

Also, in the solar heat collector 1, when the low emissivity and low solar reflectance layer 4 is prepared from a conductive ceramic, a function of reflecting the heat generated in the solar radiation absorbing layer 3 is further sufficiently ensured and the reflection of the sunlight is further reduced, so that the sunlight is capable of further surely reaching the solar radiation absorbing layer 3.

Modified Example of First Embodiment

In the description of FIG. 1, the low emissivity and low solar reflectance layer 4 is directly formed on the upper surface of the solar radiation absorbing layer 3. Alternatively, for example, though not shown, first, the low emissivity and low solar reflectance layer 4 is formed on the surface of a resin sheet such as a PET (polyethylene terephthalate) sheet and a laminated sheet made of the resin sheet and the low emissivity and low solar reflectance layer 4 is fabricated. Thereafter, the resin sheet of the laminated sheet is also capable of being attached to the surface of the solar radiation absorbing layer 3 via an adhesive. In such a case, the solar heat collector 1 includes the heat collecting board 2, the solar radiation absorbing layer 3, the resin sheet (not shown), and the low emissivity and low solar reflectance layer 4 without having any gaps between each layers.

In the description of FIGS. 2 and 3, the hot water storage portion 20 is formed at the inside of the hot water portion 7. Alternatively, for example, a hot water storage tank (not shown) is also capable of being further provided at the outside of the hot water portion 7. The hot water storage tank is connected to the water discharge port 15 via piping (not shown) and hot water that is prepared in the hot water portion 7 is discharged and saved (stored) therein. Thereafter, the hot water is supplied from the hot water storage tank to be used according to the request from users.

In the above-described description, in the solar water heater 6, the users are provided with the hot water that is prepared in the hot water portion 7 as it is. Alternatively, for example, though not shown, the heat is taken out from the hot water with a heat exchanger; other cold water is heated by the taken-out heat; and the users are also capable of being provided with the hot water that is prepared in this way. In such a case, the heat exchanger is provided in the solar water heater 6 and is disposed at the outside of the hot water portion 7. The heat exchanger is connected to the water discharge port 15 via piping. In the heat exchanger, water that is different from the heat medium is heated using the heat of the heated hot water, so that the hot water is prepared.

Furthermore, in the above-described case, the water is heated in the hot water portion 7. An object to be heated in the hot water portion 7 is not particularly limited as long as it is a heat medium To be specific, examples of the heat medium other than water include oil and antifreeze.

Furthermore, the solar water heater 6 is also capable of heating the air (gas) to obtain warm air or heating the floor (solid) using the heat medium that is heated in the hot water portion 7. In such a case, the solar water heater 6 that is one example of the solar heat heater of the present invention is served as, for example, a solar heat warm air heating system or a solar heat floor heating system.

Second Embodiment

In the second embodiment, the same reference numerals are provided for members and steps corresponding to each of those in the first embodiment, and their detailed description is omitted.

As shown in FIG. 5, a solar heat collecting multilayer sheet 21 includes a substrate sheet 10, the solar radiation absorbing layer 3, and the low emissivity and low solar reflectance layer 4.

The substrate sheet 10 is a support sheet that supports the solar radiation absorbing layer 3 and the low emissivity and low solar reflectance layer 4 and to provide the solar radiation absorbing layer 3 and the low emissivity and low solar reflectance layer 4 at the heat collecting board 2 (a phantom line). The shape in plane view of the substrate sheet 10 is formed to be the same as that in plane view of the solar heat collecting multilayer sheet 21. The outer shape of the substrate sheet 10 is not limited to the above-described shape and can be formed into an appropriate shape. To be specific, the substrate sheet 10 can be formed into, for example, a long-length sheet extending in the right-left direction. When the substrate sheet 10 is formed into a long-length sheet, the solar heat collecting multilayer sheet 21 is capable of being mass-produced by a roll-to-roll process. Also, the substrate sheet 10 is capable of being attached to the heat collecting board 2 (ref: the phantom line in FIG. 5) in various shapes.

Examples of a material that forms the substrate sheet 10 include the above-described metal material and a resin material such as polyester (to be specific, PET or the like). Preferably, a resin material is used. The substrate sheet 10 has a thickness of, for example, 5 μm or more, or preferably 10 μm or more, and of, for example, 200 μm or less, or preferably 100 μm or less.

The solar radiation absorbing layer 3 is formed on the entire upper surface of the substrate sheet 10.

The solar heat collecting multilayer sheet 21 has a thickness of, for example, 7 μm or more, or preferably 12 μm or more, and of, for example, 280 μm or less, or preferably 180 μm or less.

In order to produce the solar heat collecting multilayer sheet 21, first, the substrate sheet 10 is prepared. Next, the solar radiation absorbing layer 3 is laminated on the upper surface of the substrate sheet 10. Thereafter, the low emissivity and low solar reflectance layer 4 is laminated on the upper surface of the solar radiation absorbing layer 3.

Next, the solar heat collector 1 including the solar heat collecting multilayer sheet 21 is described with reference to FIG. 5 (ref: the phantom line).

The solar heat collector 1 includes the solar heat collecting multilayer sheet 21 and the heat collecting board 2 (ref: the phantom line) that is provided on the lower surface (the other surface in the thickness direction) of the substrate sheet 10 in the solar heat collecting multilayer sheet 21. That is, the solar heat collector 1 includes the heat collecting board 2, the substrate sheet 10, the solar radiation absorbing layer 3, and the low emissivity and low solar reflectance layer 4.

The substrate sheet 10 is provided on the upper surface of the heat collecting board 2.

In order to produce the solar heat collector 1, first, the heat collecting board 2 shown by the phantom line is prepared and subsequently, the substrate sheet 10 in the solar heat collecting multilayer sheet 21 is attached to the upper surface of the heat collecting board 2 via, for example, an adhesive or the like.

The solar heat collector 1 has a thickness of, for example, 0.1 mm or more, or preferably 0.5 mm or more, and of, for example, 5 mm or less, or preferably 2 mm or less.

Next, the solar water heater 6 using the solar heat collector 1 including the solar heat collecting multilayer sheet 21 is described with reference to FIGS. 2, 6, and 7.

As shown in FIGS. 6 and 7, the solar water heater 6 in the second embodiment is the same as that in the first embodiment, except that the structure of the solar heat collector 1 is different.

The upper board 11 corresponds to the heat collecting board 2 of the solar heat collector 1 shown in FIG. 5 and the solar heat collecting multilayer sheet 21 (to be specific, the substrate sheet 10, the solar radiation absorbing layer 3, and the low emissivity and low solar reflectance layer 4) is sequentially provided on the heat collecting board 2.

In order to fabricate the solar water heater 6, two flat plates that constitute the heat collecting board 2 of the solar heat collector 1 are prepared. Next, the substrate sheet 10 in the solar heat collecting multilayer sheet 21 is attached to the upper surface of one flat plate of the two flat plates via, for example, an adhesive. Thereafter, the two flat plates are formed by pressing to fabricate the upper board 11 and the lower board 12.

Or, first, two flat plates that constitute the heat collecting board 2 of the solar heat collector 1 are prepared. Next, the two flat plates are formed by pressing to fabricate the upper board 11 and the lower board 12. Thereafter, the substrate sheet 10 in the solar heat collecting multilayer sheet 21 is attached to the upper surface of the upper board 11 via, for example, an adhesive.

Thereafter, the upper board 11 is attached to the lower board 12 to fabricate the hot water portion 7. Thereafter, the hot water portion 7 is housed in the casing 8. Then, the protective layer 9 is laminated at the upper side of the casing 8.

Then, as shown in FIG. 5, according to the solar heat collector 1 in which the substrate sheet 10 in the solar heat collecting multilayer sheet 21 is laminated on the heat collecting board 2, the solar radiation absorbing layer 3 absorbs sunlight and heat is generated, and the heat is capable of being efficiently thermally conducted to the heat collecting board 2 via the substrate sheet 10.

When the low emissivity and low solar reflectance layer 4 absorbs the sunlight and the heat is generated, the low emissivity and low solar reflectance layer 4 is formed on the upper surface of the solar radiation absorbing layer 3, so that the heat is capable of being efficiently thermally conducted to the heat collecting board 2 via the solar radiation absorbing layer 3 and the substrate sheet 10.

Thus, as shown in FIG. 5, the solar heat collector 1 is capable of effectively using the sunlight and effectively collecting the heat.

Furthermore, the solar water heater 6 shown in FIG. 7 includes the above-described solar heat collector 1, so that water is capable of being efficiently heated.

Furthermore, the upper board 11 is capable of constituting the solar heat collector 1 only by attaching the solar heat collecting multilayer sheet 21 to the upper board 11 and thereafter, the solar water heater 6 is capable of being fabricated. Thus, the solar heat collector 1 and the solar water heater 6 are capable of being easily produced.

EXAMPLES

Values in Examples shown in the following can be replaced with the values (that is, the upper limit value or the lower limit value) described in the above-described embodiment.

Example 1 Fabrication of Solar Heat Collector

An aluminum board (a thickness of 0.5 mm) as a heat collecting board was prepared and next, a black coating material was applied to the upper surface of the heat collecting board to form a solar radiation absorbing layer (a thickness of 30 μm). Thereafter, an ITO film (a thickness of 250 nm) as a low emissivity and low solar reflectance layer was formed on the upper surface of the solar radiation absorbing layer by a sputtering method. In this way, a solar heat collector including the heat collecting board, the solar radiation absorbing layer, and the low emissivity and low solar reflectance layer was fabricated (ref: FIG. 1).

Example 2

A solar heat collector was fabricated in the same manner as that in Example 1, except that the thickness of the ITO film was changed to 350 nm.

Example 3

A solar heat collector was fabricated in the same manner as that in Example 1, except that the thickness of the ITO film was changed to 550 nm.

Example 4

A solar heat collector was fabricated in the same manner as that in Example 1, except that an FTO film (a thickness of 250 nm) as a low emissivity and low solar reflectance layer was formed by a sputtering method instead of the ITO film.

Example 5

A solar heat collector was fabricated in the same manner as that in Example 1, except that an ATO film (a thickness of 250 nm) as a low emissivity and low solar reflectance layer was formed by a sputtering method instead of the ITO film.

Example 6

A solar heat collector was fabricated in the same manner as that in Example 1, except that an IZO film (a thickness of 250 nm) as a low emissivity and low solar reflectance layer was formed by a sputtering method instead of the ITO film.

Example 7 Fabrication of Solar Heat Collecting Multilayer Sheet

A PET film (a thickness of 100 μm) as a substrate sheet was prepared and next, a black coating material was applied to the upper surface of the substrate sheet to form a solar radiation absorbing layer (a thickness of 30 μm). Thereafter, an ITO film (a thickness of 250 nm) as a low emissivity and low solar reflectance layer was formed on the upper surface of the solar radiation absorbing layer by a sputtering method. In this way, a solar heat collecting multilayer sheet including the substrate sheet, the solar radiation absorbing layer, and the low emissivity and low solar reflectance layer was fabricated (ref: a solid line in FIG. 5).

(Fabrication of Solar Heat Collector)

The substrate sheet in the solar heat collecting multilayer sheet was attached to the upper surface of an aluminum board (a thickness of 0.5 mm) as a heat collecting board via an adhesive. In this way, a solar heat collector including the heat collecting board and the solar heat collecting multilayer sheet was fabricated (ref: the phantom line in FIG. 5).

Comparative Example 1

A solar heat collector was fabricated in the same manner as that in Example 1, except that a low emissivity and low solar reflectance layer was not formed (ref: FIG. 9C).

Comparative Example 2

A solar heat collector was fabricated in the same manner as that in Example 1, except that an SiO₂ film (a thickness of 250 nm, an insulating ceramic) as a high emissivity and low solar reflectance layer was formed by a sputtering method instead of the low emissivity and low solar reflectance layer (the ITO film).

Comparative Example 3

A solar heat collector was fabricated in the same manner as that in Example 1, except that an APC silver alloy film (a thickness of 40 nm, a metal layer) as a low emissivity and high solar reflectance layer was formed by a sputtering method instead of the low emissivity and low solar reflectance layer (the ITO film).

Comparative Example 4

A solar heat collector (1) was fabricated in the same manner as that in Example 1, except that a low emissivity and low solar reflectance layer (4) was not disposed on the upper surface of a solar radiation absorbing layer (3) but was disposed at spaced intervals to the upper side thereof (ref: FIG. 8).

To be specific, as shown in FIG. 8, the low emissivity and low solar reflectance layer (4) was formed on the lower surface of a glass plate (26) (a thickness of 1 mm) in the same manner as that in Example 1. The low emissivity and low solar reflectance layer (4), the glass plate (26), and the solar radiation absorbing layer (3) were disposed, while supported by support materials (32) or the like, so that a gap (10 mm) was formed between the low emissivity and low solar reflectance layer (4) and the solar radiation absorbing layer (3).

In this way, the solar heat collector (1) including a heat collecting board (2), the solar radiation absorbing layer (3), and the low emissivity and low solar reflectance layer (4) and having a gap (30) between the solar radiation absorbing layer (3) and the low emissivity and low solar reflectance layer (4) was fabricated.

(Evaluation)

(Surface Temperature)

A heat collecting box (27) shown in FIGS. 9A to 9D was fabricated using a solar heat collector.

That is, a bottomed box (25) prepared from a heat insulating material that had a thickness of 20 mm and having an opening upwardly was prepared. The size of the box (25) is as follows: an outer shape in plane view of 140 mm×140 mm, an opening (an inner shape) in plane view of 100 mm×100 mm, a height of the box of 40 mm, and a depth of the inside of the box of 20 mm.

Separately, the solar heat collector (1) was trimmed into a size of 100 mm×100 mm. The heat collecting board (2) in the trimmed solar heat collector (1) was allowed to adhere to the upper surface of the bottom wall of the box (25) via an adhesive.

Next, the upper end portion of the opening was covered with a float glass (26) having a thickness of 4 mm. In this way, the heat collecting box (27) was fabricated.

Next, the surface temperature of the solar heat collector (1) (the low emissivity and low solar reflectance layer (4)) at the time of applying pseudo sunlight to the heat collecting box (27) at an irradiation strength of 1 SUN (AM 1.5) for 20 minutes using a solar simulator (XES 450-S1, manufactured by SAN-EI ELECTRIC CO., LTD.) was measured with a thermocouple. In Comparative Examples 1 and 4, the surface temperature of the solar radiation absorbing layer (3) was measured.

A heat collecting box in which the solar heat collector (1) in Examples 1 to 6 and Comparative Examples 2 and 3 is measured is shown in FIG. 9A. A heat collecting box in which the solar heat collector (1) in Example 7 is measured is shown in FIG. 9B. A heat collecting box in which the solar heat collector (1) in Comparative Example 1 is measured is shown in FIG. 9C. A heat collecting box in which the solar heat collector (1) in Comparative Example 4 is measured is shown in FIG. 9D.

The results are shown in Table 1.

(Emissivity)

The emissivity of the low emissivity and low solar reflectance layer (4) in the solar heat collector (1) was measured using an emissivity measuring device (manufactured by Devices and Services Company).

The results are shown in Table 1.

(Solar Reflectance)

The solar reflectance of the low emissivity and low solar reflectance layer (4) in the solar heat collector (1) was measured using a spectrophotometer (U-4100, manufactured by Hitachi High-Technologies Corporation). The solar reflectance was measured as a solar reflectance in a region of near infrared ray (780 to 2500 nm).

The results are shown in Table 1.

TABLE 1 Thickness of Low Low Emissivity and Emissivity and Low Low Solar Solar Reflectance Solar Reflectance Surface Reflectance Layer Layer (nm) Emissivity (%) Temperature (° C.) Ex. 1 ITO 250 0.43 8.0 124 Ex. 2 ITO 350 0.42 8.6 126 Ex. 3 ITO 550 0.41 9.0 128 Ex. 4 FTO 250 0.47 7.0 123 Ex. 5 ATO 250 0.46 7.5 123 Ex. 6 IZO 250 0.50 7.7 121 Ex. 7*¹ ITO 250 0.44 6.4 125 Comp. Ex. 1 Absence — — 4.7 114 Comp. Ex. 2 SiO₂*³ 250 0.87 3.5 115 Comp. Ex. 3 SilverAlloy*⁴  40 0.12 73.5 88 Comp. Ex. 4*² ITO 250 0.43 8.0 110 *¹Having substrate sheet *²Having gap between solar reflectance layer and low emissivity and low solar reflectance layer *³High emissivity and low solar reflectance layer *⁴Low emissivity and high solar reflectance layer

While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed as limiting the scope of the present invention. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims. 

What is claimed is:
 1. A solar heat collector comprising: a heat collecting board, a solar radiation absorbing layer provided at one surface in a thickness direction of the heat collecting board, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.
 2. The solar heat collector according to claim 1, wherein the low emissivity and low solar reflectance layer has an emissivity of 0.75 or less and has a solar reflectance of 50% or less.
 3. The solar heat collector according to claim 1, wherein the low emissivity and low solar reflectance layer is prepared from a conductive ceramic.
 4. A solar heat heater comprising: a solar heat collector, wherein the solar heat collector comprises: a heat collecting board, a solar radiation absorbing layer provided at one surface in a thickness direction of the heat collecting board, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.
 5. A solar heat collecting multilayer sheet comprising: a substrate sheet, a solar radiation absorbing layer provided at one surface in a thickness direction of the substrate sheet, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.
 6. The solar heat collecting multilayer sheet according to claim 5, wherein the low emissivity and low solar reflectance layer has an emissivity of 0.75 or less and has a solar reflectance of 50% or less.
 7. The solar heat collecting multilayer sheet according to claim 5, wherein the low emissivity and low solar reflectance layer is prepared from a conductive ceramic.
 8. A solar heat collector comprising: a solar heat collecting multilayer sheet including: a substrate sheet, a solar radiation absorbing layer provided at one surface in a thickness direction of the substrate sheet, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer and a heat collecting board provided at the other surface in the thickness direction of the substrate sheet in the solar heat collecting multilayer sheet.
 9. A solar heat heater comprising: a solar heat collector, wherein the solar heat collector comprises: a solar heat collecting multilayer sheet including: a substrate sheet, a solar radiation absorbing layer provided at one surface in a thickness direction of the substrate sheet, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer and a heat collecting board provided at the other surface in the thickness direction of the substrate sheet in the solar heat collecting multilayer sheet.
 10. A solar heat heater used as a solar water heater comprising: a solar heat collector, wherein the solar heat collector comprises: a heat collecting board, a solar radiation absorbing layer provided at one surface in a thickness direction of the heat collecting board, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer.
 11. A solar heat heater used as a solar water heater comprising: a solar heat collector, wherein the solar heat collector comprises: a solar heat collecting multilayer sheet including: a substrate sheet, a solar radiation absorbing layer provided at one surface in a thickness direction of the substrate sheet, and a low emissivity and low solar reflectance layer provided at one surface in the thickness direction of the solar radiation absorbing layer and a heat collecting board provided at the other surface in the thickness direction of the substrate sheet in the solar heat collecting multilayer sheet. 